1. Field of the Invention
The present invention relates to a test carrier used when a semiconductor device having terminals on its surface such as a bare chip is tested, and more particularly, to a test carrier with less thickness and with improved connectability and to a method of mounting a semiconductor device on the test carrier.
2. Description of the Related Art
Conventionally, a test carrier is structured to receive a semiconductor device such as a bare chip such that the electric characteristics of the bare chip (semiconductor device) can be tested with the chip being handled similarly to a packaged product.
As disclosed in Japanese Patent Application Laid-open No. Hei 10-65069 (laid open on Mar. 6, 1998), a test carrier is typically formed of a contact sheet (a thin circuit substrate) to be connected to a bare chip when the bare chip is received, a pressing member having a spring for pressing the bare chip against the contact sheet with predetermined pressure, and a housing for receiving or retaining the contact sheet and the pressing member. The contact sheet of a test carrier has bumps such as of solder for connecting to electrode pads of a bare chip. The connection is made by hard contact between the electrode pads of the bare chip and the bumps of the contact sheet caused by the pressing member.
The electric characteristics are tested by connecting the electrodes of the contact sheet of the test carrier to testing equipment.
In case of such a conventional test carrier, since the electrode pads of the bare chip are made of thin film of aluminum or copper, their surfaces are liable to natural oxidation. This causes a problem in that, in case that electrode pads of a bare chip and bumps of a contact sheet are connected, stable test can not be carried out simply by pressing the electrode pads and the bumps with the pressing member, since the connection is poor due to a natural oxide film on the surface. Thus, a need exists for providing stable contact between a bare chip and a contact sheet within a test carrier.
On the other hand, it is necessary to structure a test carrier such that a bare chip such as an LSI, a semiconductor device, or the like can be tested in a state similar to that of a packaged product.
More particularly, in testing a bare chip, in order to lower the cost, it is necessary to use various testing apparatus used in testing a packaged product as it is or with the minimum modification. Thus, a test carrier the size of which is almost the same as that of an ordinary packaged IC or LSI is needed.
As described in the above, a test carrier is required to achieve miniaturization and thinning of the respective parts forming the test carrier, and at the same time, stable contact with a bare chip therein.
Further, in case of a pressing member in a conventional test carrier, the pressing force of a spring necessary between a bare chip and the contact sheet is 9-20 g (gram) per bump. It follows that, if the number of the bumps in the contact sheet is 70, the pressing force totals up to 1.3 kg at the maximum. Taking into consideration the dimensional tolerance of the test carrier, pressing force larger than or equal to 1.3 kg is necessary. The pressing force is generated by the spring, and thus, springs having a large spring constant are necessary.
However, in case that conventional springs that meet the Japanese Industrial Standards, for example, are used, in order to obtain sufficient spring characteristics (pressing force and a spring constant), the size of the springs must be large, which limits miniaturization of the test carrier. Conventionally, using a nonstandardized spring is out of the question.
Further, conventionally, a test carrier is entirely (except for the contact sheet) formed of a resin material, but, since the resin material is liable to distortion when pressed by springs, attempt to decrease the distortion makes it difficult to thin the test carrier.
Accordingly, an object of the invention is to provide a test carrier which can materialize stable contact between a semiconductor device such as a bare chip and a contact sheet, and to provide a method of mounting a semiconductor device thereon.
Another object of the invention is to provide a test carrier which achieves miniaturization and thinning thereof, and at the same time, stable contact with a semiconductor device therein.
For the purpose of testing, a semiconductor device having first terminals on the surface is mounted on a test carrier according to the present invention. The test carrier has a carrier base, a contact sheet disposed on the carrier base, a pressure applying member, and a securing member. The contact sheet is opposed to the semiconductor device, and has second terminals in contact with and connected to the first terminals of the semiconductor device and external electrodes for testing. The pressure applying member applies predetermined contact pressure between the first terminals of the semiconductor device and the second terminals of the contact sheet. The securing member secures the contact sheet on the carrier base.
The present invention is particularly characterized in that the center of thermal expansion of the contact sheet secured by the securing member is offset from all the second terminals of the contact sheet.
With this structure, due to the difference between the coefficient of thermal expansion of the second terminals of the contact sheet and that of the first terminals of the bare chip, the second terminals of the contact sheet (or the first terminals of the semiconductor device) slightly move, scraping or scrubbing the surface of all the first terminals of the semiconductor device (or of all the second terminals of the contact sheet). As a result, an oxide film formed on the surfaces of all the first terminals (or of all the second terminals) is removed.
According to another aspect of the present invention, a test carrier comprises a carrier base, a contact sheet disposed on the carrier base, opposed to a semiconductor device, and having second terminals in contact with and connected to first terminals of the semiconductor device and external electrodes for testing, a pressure applying member for applying predetermined contact pressure between the first terminals and the second terminals, and a securing member for securing the contact sheet on the carrier base. Further, the securing member secures the carrier base and the contact sheet at two or more securing points, and the center of a figure formed by linking the securing points is offset from all the second terminals.
The present invention has an effect similar to that of the invention described in the above.
A mounting method according to the present invention is a method of mounting on a test carrier a semiconductor device to be tested having first terminals on the surface. The mounting method uses a test carrier including a contact sheet opposed to the semiconductor device and having second terminals in contact with and connected to the first terminals of the semiconductor device and external electrodes for testing. Further, the securing positions of a securing member for securing the contact sheet on the carrier base of the test carrier are determined such that the center of thermal expansion of the contact sheet is offset from all the second terminals of the contact sheet, and the semiconductor device and the test carrier are retained with predetermined contact pressure applied between the first terminals and the second terminals. With the retaining state being maintained, by heating at least the contact sheet, the contact sheet is expanded to form scrapes at all the contact portions between the first terminals and the second terminals.